Mea's Castle
Mea's Castle is a Metroidvania-like Game: You're a little Adventurer and your Goal is to find the 'Cup of Hope'. You can run and jump, and soon you will find some Artifacts that'll give you more Abilities.
?? - Move
? + ?? - Crouch
(Z) - Jump
(X) + ? - Use the last Powerup
Warning
This Game is difficult. If you're not a Fan of Jump'n Run-like Games, I think it will be too frustrating^^. There are still Checkpoints basically everywhere, but it's still not easy to beat that Game. Expect to die a lot while playing this^^.
Credits
Thanks to

@Gruber for the Music 'Eyes in the Dark' and 'Flight of Icarus' (both with slight Remixes) from Pico-8 Tunes Volume 2 .
Youtuber Dev Quest and his Video Efficient Tilesets in Pico-8 Tutorial
@Krystman for his Cartridge 'Sample Code: Screenshake and Fading' and all the other Videos and Tutorials.
Youtuber hh7x6 and his Speedrun-Video.
Of course: Thanks to you for playing! :)

Other stuff
Also, if you like to cheat, you can use